In addition to genetic alterations, epigenetic changes- heritable changes in gene expression or cellular phenotypes without DNA alterations - are a major driving force for prostate cancer events. In contrast to great advance in our understanding of genetic alterations, the molecular basis underlying epigenetic changes remains to be further explored. Histone lysine (K) methylation has emerged as a hallmark associated with epigenetic regulation of gene expression. In particular, trimethylation at histone H3 lysine 4 (trimethyl H3K4) is a genome-wide epigenetic signal that occupies and affects 75% of all the gene-regulatory regions. Alterations in the global and local profile of this key epigenetic signal commonly occur in many advanced prostate tumors and are associated with oncogene activation and tumor suppressor gene inactivation. However, it is unknown how such alterations in trimethyl H3K4 profiles occur in prostate cancer cells. The long-term objective of the proposed study is to characterize the molecular mechanisms responsible for epigenetic events associated with alterations in trimethyl H3K4 profiles in advanced prostate cancer. In a recent breakthrough study, we identified JARID1d as a novel male-specific histone demethylase that is capable of removing methyl groups (demethylating) from trimethyl and dimethyl H3K4 (Cell, 2007). In addition, our bioinformatic analysis showed that JARID1d levels are dysregulated in advanced prostate tumors, indicating an importance role for JARID1d in epigenetic changes involving alterations in trimethyl H3K4 during prostate cancer events. Our preliminary studies identified novel JARID1d-associated proteins that are likely involved in the recruitment and the molecular regulation of JARID1d. Based on these exciting, definitive findings, our central hypothesis is that dysregulation of JARID1d plays a key role in epigenetic alterations in trimethyl H3K4 profiles at JARID1d target genes and consequently contributes to prostate cancer events. In the proposed study, we focus on understanding the role and regulation of JARID1d in epigenetic changes associated with trimethyl H3K4 alterations during prostate cancer events. Specific Aims are to 1) Determine the chromatin locations and recruitment mechanisms of JARID1d; 2) Elucidate the molecular mechanisms that regulate JARID1d-mediated demethylation; 3) Determine the role of JARID1d in prostate tumor progression and metastasis. Our proposed studies are fundamental to understanding the molecular mechanisms underlying a common epigenetic event, i.e., alterations in trimethyl H3K4 profiles, in advanced prostate tumors and will uncover an unprecedented role for the epigenetic modifier JARID1d in prostate tumor progression and invasion.